JP2011045013A - Sound signal processor, fm receiver, and method of processing sound data - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sound signal processor and an FM receiver capable of performing interpolation processing smoothly without abrupt change of a sound level when an abnormality of a sound signal is detected. <P>SOLUTION: The sound signal processor includes a demodulator which demodulates a sound signal, an abnormality detector which detects an abnormality of the sound signal, a holder which holds the sound signal before detection of the abnormality while the demodulator inputs a demodulating sound signal and the abnormality detector detects at least the abnormality, and a weighted averaging processor which inputs a sound signal newly demodulated by the demodulator and the sound signal held by the holder and outputs a signal with a gradual change from the sound signal held by the holder to the sound signal demodulated by the demodulator after recovery from the abnormality. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an audio signal processing device, an FM receiving device, and an audio data processing method thereof. In particular, the present invention relates to an interpolating process when an abnormality occurs in received data with respect to audio reception of TV broadcasting.

  2. Description of the Related Art Conventionally, FM receivers mounted on mobile bodies such as automobiles have a multipath failure caused by reflection of electromagnetic waves from obstacles such as mountains and buildings around when audio signals are received. It is known that the demodulated signal becomes abnormal.

  Patent Document 1 describes a conventional FM receiver that interpolates a missing signal at the time of abnormality for a multipath failure. 9A is a block diagram of the conventional FM receiver described in Patent Document 1, and FIG. 9B is an explanatory diagram of interpolation using an interpolation signal.

  In FIG. 9A, when the signal is normally received, the intermediate frequency signal 1 is FM demodulated by the discriminator (FM demodulator) 2, and the audio signals from the LPFs 6 and 7 subjected to stereo demodulation are converted into the electronic switcher 47. , 48, the left ear signal 10 and the right ear signal 11 are output. Further, the amplitude of the intermediate frequency signal 1 is detected by an envelope detector 41 and compared with a reference value 43 by an amplitude comparison circuit 42. When the amplitude detection signal is smaller than the reference value 43, a control pulse is generated by a control pulse generator 44. To switch the electronic switch charts 45, 46, 47, and 48 from the a side to the b side to perform interpolation. Interpolation is performed by repeatedly outputting the demodulated signal before switching at a predetermined cycle by the delay elements 49 and 50.

  As shown in FIG. 9B, when interpolation is performed from t1 to t2, the audio signal (A) in the period T from t0 to t1 immediately before t1 is repeatedly output (B) from t1 to t2. Interpolate.

  Further, Patent Document 2 describes an FM signal processing apparatus that generates an output signal by attenuating an input signal at the time of current sampling when noise due to multipath noise is detected.

JP-A-6-152551 JP 2003-283349 A

  The following analysis is given by the present invention. The abnormality of the demodulated audio signal also occurs when the FM signal is overmodulated. If the FM signal is modulated beyond the frequency band, it is out of the range of the band filter of the receiver, and voice information cannot be extracted.

  Further, when the noise period is interpolated as in Patent Document 1, a difference in level between the interpolated signal and the normal signal appears particularly when the interpolated signal is returned to the normal signal, and an audible sound is generated. There is a case.

  An audio signal processing device according to one aspect of the present invention inputs a demodulation unit that demodulates an audio signal, an abnormality detection unit that detects that the audio signal becomes abnormal, and an audio signal that the demodulation unit demodulates. A holding unit that holds a sound signal before detecting an abnormality, a sound signal that is newly demodulated by the demodulation unit, and a sound signal that is held by the holding unit, at least during a period in which the abnormality detection unit detects the abnormality And a specific gravity average processing unit that gradually switches from the audio signal held by the holding unit to the audio signal demodulated by the demodulation unit and outputs the audio signal after recovering from the abnormality.

  An FM signal receiver according to another aspect of the present invention includes a tuner that receives an FM signal and outputs an intermediate frequency signal, an AD converter that converts the intermediate frequency signal into a digital intermediate frequency signal, and the digital intermediate frequency. An FM detector for detecting a digital audio signal from the signal, an intermediate frequency abnormality detection unit for detecting an abnormality of the digital intermediate frequency signal, and an intermediate frequency abnormality detection unit before detecting the abnormality while detecting the abnormality A holding unit for holding the digital audio signal, and a specific gravity average process for gradually switching the digital audio signal held by the holding unit after the recovery from the abnormality to a digital audio signal newly detected by the FM detector and outputting it And a DA converter that converts the digital audio signal into an analog audio signal.

  The audio data processing method in the audio signal processing device according to still another aspect of the present invention is such that when there is no abnormality in the audio data signal, the audio data signal is demodulated and output, and the audio data signal is abnormal Outputs the signal demodulated before becoming abnormal, and when the abnormality of the audio data signal is recovered, the signal demodulated before becoming abnormal and the signal demodulated after the abnormality is recovered are weighted respectively. And the weighting ratio is recovered from the signal demodulated before becoming abnormal, and then the error is recovered from the demodulated signal before becoming abnormal by gradually shifting to the demodulated signal after the abnormality is recovered. Smoothly transition to the demodulated signal.

  According to the present invention, when an audio signal becomes abnormal, the audio signal before the abnormality is continuously output, and after recovering from the abnormality, the specific gravity average is taken to recover from the abnormality before the abnormality. Since the sound signal is gradually switched to the later sound signal, even if the sound signal becomes abnormal, it is possible to alleviate the sense of discomfort in hearing.

It is a block diagram of the whole FM receiver by one Example of this invention. (A) Drawing explaining frequency spectrum distribution of video signal and audio signal in TV signal receiving apparatus, (b) Drawing explaining state where FM modulation width of audio signal is within BPF band, (c) It is drawing explaining the state where the FM modulation width of an audio signal exceeds the BPF band. FIG. 2A is a waveform diagram of a normal intermediate frequency signal waveform and FIG. 2B is a waveform diagram of an abnormal intermediate frequency signal waveform in the FM receiver. (A) an abnormal intermediate frequency signal waveform, (b) an audio signal waveform when the audio signal is demodulated from the abnormal intermediate frequency signal, (c) an audio signal waveform obtained by compressing the time axis of (b), d) When the abnormality occurs in the intermediate frequency signal, it is a sound signal waveform diagram when the sound signal before the abnormality is maintained. In one embodiment of the present invention, (a) a waveform diagram of an abnormal intermediate frequency signal, (b) an output signal waveform diagram of the demodulator, and (c) an output signal waveform diagram of the demodulator with an expanded time axis range. (D) is an output signal waveform diagram of the selection unit. It is a wave form image figure of specific gravity average processing in the present invention. It is a figure which shows the relationship between FM detection output waveform and specific gravity average output waveform after recovering from abnormality in one Example. It is a flowchart explaining the processing method of the audio | voice data in one Example. It is (a) block diagram of the conventional FM receiver described in patent document 1, and (b) is explanatory drawing of the interpolation by an interpolation signal.

  Regarding the embodiment of the present invention, an overall outline will be described first. In the description of the outline, the drawings and the reference numerals of the drawings are shown as examples of the embodiments, and the variations of the embodiments according to the present invention are not limited thereby.

  As shown in FIG. 1 as an example, an audio signal processing device according to an embodiment of the present invention includes a demodulation unit 101 that demodulates an audio signal 134, an abnormality detection unit 102 that detects that the audio signal 134 becomes abnormal, An audio signal 134 demodulated by the demodulator 101 is input, and a holding unit 103 that holds an audio signal before detecting an abnormality at least during a period when the abnormality detector 102 detects an abnormality, and a demodulator 101 newly The audio signal 134 to be demodulated and the audio signal 137 held by the holding unit 103 are input, and after recovering from the abnormality, the audio signal 137 held by the holding unit 103 is gradually changed to the audio signal 134 demodulated by the demodulation unit 101. And a specific gravity average processing unit 107 for switching and outputting. When an abnormality is detected, the audio is switched from the audio signal demodulated by the demodulation unit 101 to the holding unit 103 that holds the audio signal demodulated by the demodulation unit 101. Further, when recovering from the abnormality, the specific gravity average processing unit 107 gradually switches from the audio signal held by the holding unit 103 to the audio signal demodulated by the demodulating unit 101. Can be relaxed.

  Further, the demodulation unit 101 detects and demodulates the audio signal 134 from the FM-modulated audio intermediate frequency signal 133, and the abnormality detection unit 102 inputs the audio intermediate frequency signal 133 and the audio signal 134 becomes abnormal. May be detected. Furthermore, processing required for detecting that the audio signal 134 becomes abnormal after the abnormality detection unit 102 inputs the audio intermediate frequency signal 133 from the processing time required for the demodulation unit 101 to demodulate the audio signal from the audio intermediate frequency signal 133. The time is short, and the holding unit 103 holds an audio signal immediately after the abnormality detecting unit 102 detects an abnormality and immediately before the demodulating unit 101 starts outputting an abnormal audio signal.

  Further, the specific gravity average processing unit 107 weights the audio signal 137 held by the holding unit 103 and the audio signal 134 demodulated by the demodulation unit 101, and the weighting specific gravity from the audio signal 137 held by the holding unit 103. The demodulator 101 gradually shifts to the audio signal 134 to be demodulated, takes an average, and outputs the averaged audio signal 138.

  Furthermore, three audio signals (134, 137, 138) of the audio signal 134 newly demodulated by the demodulator 101, the audio signal 137 held by the holding unit 103, and the audio signal 138 output by the specific gravity average processing unit 107. ) To select and output one of them. When the abnormality detection unit 102 has not detected an abnormality, the selection unit 106 selects and outputs the audio signal 134 that the demodulation unit 101 newly demodulates. While the abnormality detection unit 102 detects an abnormality, the audio signal held by the holding unit 103 is selected and output, and after the abnormality detection unit 102 detects recovery from the abnormality, the specific gravity is maintained for a certain period. The audio signal output by the average processing unit 107 is selected and output.

  In addition, when the abnormality detection unit 102 has not detected an abnormality, the holding unit 103 updates the data held by the audio signal 134 newly demodulated by the demodulation unit 101, and the specific gravity average processing unit 107 is updated by the holding unit 103. When the process of gradually switching to the audio signal 134 demodulated by the demodulator 101 is output from the audio signal 137 held by the demodulator 101, the data held by the audio signal 138 output by the specific gravity processing average processor 107 is updated. . Furthermore, the holding unit 103 updates the data by the preselection unit 104 that selects the audio signal 134 output from the demodulation unit 101 and the audio signal 135 output from the selection unit 106, and the audio signal selected by the preselection unit 104. Flip-flop circuit 105. The preselection unit 104 selects the audio signal 134 output from the demodulation unit 101 when the abnormality detection unit 102 has not detected an abnormality. In addition, the preselection unit 104 gradually switches from the audio signal 137 of the holding unit 103 to the audio signal 134 of the demodulation unit 101 when the abnormality detection unit 102 detects an abnormality and the specific gravity average processing unit 107 The audio signal output from the selection unit 106 when the user is in the middle is selected.

  The abnormality detection unit 102 receives the audio intermediate frequency signal 133 and detects an abnormality when the amplitude of the audio intermediate frequency signal 133 is abnormally small. The abnormality detection unit 102 detects an abnormality when the amplitude of the audio intermediate frequency 133 is continuously lower than a predetermined threshold value a predetermined number of times. The audio signal processing apparatus is integrated and formed on one semiconductor substrate. In other words, all of the above-described configuration requirements can be integrated into one chip as a semiconductor integrated circuit.

  As an example, as shown in FIG. 1, the FM signal receiving apparatus 100 according to an embodiment of the present invention receives a FM signal 131 and outputs an intermediate frequency signal 132, and the intermediate frequency signal 132 is converted into a digital intermediate frequency. An A / D converter 113 that converts the signal 133, an FM detector 101 that detects the digital audio signal 134 from the digital intermediate frequency signal 133, an intermediate frequency abnormality detector 102 that detects an abnormality in the digital intermediate frequency signal 133, While the intermediate frequency abnormality detection unit 102 detects an abnormality, the holding unit 103 holds the digital audio signal 134 before detection, and the digital audio signal 137 held by the holding unit 103 after recovering from the abnormality, FM to FM The detector 101 gradually switches to the newly detected digital audio signal 134 and outputs it. It comprises a weighted average processing unit 107, a D / A converter 114 for converting the digital audio signal 135 to an analog audio signal 136, a.

  Further, the A / D converter 113, the FM detector 101, the intermediate frequency abnormality detection unit 102, the holding unit 103, the specific gravity average processing unit 107, and the D / A converter 114 are provided on one semiconductor substrate. It is integrated and formed. In other words, the above configuration may be included in one semiconductor integrated circuit 120.

  Further, as shown in FIG. 8, the audio data processing method in the audio signal processing apparatus according to the embodiment of the present invention has no abnormality in the audio data signal (the data signal A / D converted in step S1) as shown in FIG. When (No in step S3), the audio data signal is demodulated and output (steps S4 to S6). When the audio data signal is abnormal (in the case of step S3 Yes), it is demodulated before becoming abnormal. When the signal is output (steps S7 to S10) and the abnormality of the audio data signal is recovered (Yes in step S11), the signal demodulated before becoming abnormal (stored in the F / F 105 by step S5 before becoming abnormal) Data) and a signal demodulated after recovery from the abnormality (data demodulated in step S15) are weighted and added (step S16), respectively. By gradually shifting to the demodulated signal after the abnormality has been recovered from the signal demodulated before the abnormality becomes the demodulated ratio, the demodulated signal is recovered after the abnormality is recovered from the signal demodulated before the abnormality. Make a smooth transition. In the embodiment shown in FIG. 8, the data stored in the F / F 105 is updated by the result of the specific gravity average calculation (step S16) in step S17, but is stored in the F / F 105 being updated. The data thus obtained is data obtained by weighting and adding a signal demodulated before becoming abnormal and a signal demodulated after the abnormality is recovered. Therefore, the specific gravity average calculation in step S16 is not simply weighted and added to the signal demodulated before becoming abnormal and the signal demodulated after the abnormality is recovered. A signal demodulated before becoming and a signal demodulated after recovery from the abnormality are weighted and added.

  Next, before describing a more specific embodiment, the overmodulation of the FM signal already described as the subject of the present invention will be described in a little more detail. FIG. 2A illustrates the frequency spectrum distribution of the video signal and the audio signal in the TV signal receiving apparatus. As is well known, a TV broadcast signal is transmitted by mixing a video signal and an audio signal in a predetermined frequency band (channel) and placing them on a carrier wave. The TV tuner receives a broadcast signal and extracts a video signal and an audio signal from a desired frequency band (channel). As shown in FIG. 2A, the audio signal has a frequency band between the frequency band of the video signal of the own channel and the frequency band of the video signal of the next channel adjacent thereto. That is, in FIG. 2A, 201 is the video signal of the own channel, 202 is the audio signal of the own channel, 203 is the video signal of the next channel, and 204 is the audio signal of the next channel. The audio signal 202 of the own channel is located in an intermediate frequency band between the video signal 201 of the own channel and the video signal 203 of the next channel. Therefore, the band pass filter BPF is used to extract the audio signal of the own channel while distinguishing it from other signals of adjacent frequencies. The frequency band extracted by the bandpass filter BPF is set to be narrower than the FM modulation width of the audio signal and so as to cut off the signal in the adjacent frequency band. If it has such a bandpass filter characteristic, only the audio signal of the selected channel can be extracted. In FM modulation, it is known that the volume level is controlled not by amplitude but by FM modulation width. When the volume is high, the FM modulation width is widened, and when the volume is low, the FM modulation width is also small.

  Here, in a country where the country is large but antenna installation is difficult and the number of installations is small, in order to reduce the influence of noise and skip broadcast radio waves, FM modulation may be excessively carried on a carrier wave. However, in the case of excessively modulated audio, the TV tuner may output an abnormal audio signal. It is presumed that the TV tuner sometimes fails to extract the audio signal.

  FIGS. 2B and 2C are diagrams for explaining the band of the band-pass filter and the FM modulation width of the audio signal. FIG. 2B shows a case where the FM modulation width is within the bandpass filter band, and FIG. 2C shows a case where the FM modulation width exceeds the bandpass filter band. .

  For example, when the frequency of 5.5 MHz is FM-modulated at 27 kHz, the spectrum is located in the frequency band of 5.5 MHz ± 27 kHz, and the spectrum does not become sharp but has a horizontal spread. When extracting with the normal BPF, the entire spectrum spread horizontally is extracted with the BPF as shown in FIG. However, if FM modulation is applied excessively, the spread of the spectrum becomes too large, exceeding the BPF band. Then, as shown in FIG. 2C, there is a frequency band 251 that is FM-modulated beyond the bandpass filter BPF band, and an audio signal in this range cannot be extracted.

  When FM modulation is performed within the bandpass filter BPF as shown in FIG. 2B, the FM-modulated audio signal can be normally extracted as shown in FIG. On the other hand, when overmodulation is performed as shown in FIG. 2C and FM modulation is performed beyond the band of the bandpass filter BPF, overmodulation occurs as shown in FIG. Where the amplitude is abnormally small, the audio signal almost disappears and becomes noise. When the TV tuner cannot cope with the overmodulated audio signal, an abnormal signal is output, and the abnormal signal is input to the FM detector.

  FIG. 4 shows a waveform when a signal that has failed to extract an audio signal overmodulated by such a tuner is FM demodulated by an FM detector. FIG. 4A shows a waveform of an intermediate frequency signal that has failed to be extracted due to overmodulation. In FIG. 4A, the amplitude is abnormally small due to overmodulation during the period from T1 to T2. When such an intermediate frequency signal is FM demodulated by the FM detector, an audio signal as shown in FIG. 4B is obtained. Since the processing time required for the demodulation process by the FM detector (demodulation unit) is related, an abnormal intermediate frequency signal in the section T1 to T2 in FIG. 4 (a) is voiced in the section T3 to T4 in FIG. 4 (b). Output as signal noise. FIG. 4C is a waveform diagram obtained by compressing the time axis of FIG.

  In the case of an FM-modulated audio signal, the volume (the amplitude after demodulation) increases as the modulation increases. Therefore, in the case of overmodulation, noise enters at a position where the volume is maximized, and the noise becomes more noticeable. Therefore, as shown in FIG. 4 (d), when the voice signal is detected to be abnormal, the abnormal section is interpolated by maintaining the voice immediately before it becomes abnormal, and when the voice signal returns to normal, Switching from the interpolated audio signal to the audio signal demodulated by the demodulator can be considered. In FIG. 4 (d), the demodulator can demodulate the normal audio signal by maintaining and interpolating the audio signal immediately before it becomes abnormal in the section from T3 to T4 where the demodulator will output an abnormal audio signal. Thus, the audio signal demodulated by the demodulator after timing T4 is output. Even when such processing is performed, the level of the signal changes suddenly when the newly demodulated audio signal is switched from the audio signal interpolated at the timing T4, and an audible sound (noise) is generated. .

  Next, an embodiment of the present invention that solves the above problems will be described in detail.

  FIG. 5 shows, in one embodiment of the present invention, (a) a waveform diagram of an abnormal intermediate frequency signal, (b) an output signal waveform diagram of the demodulator, and (c) a demodulator with an expanded time axis range. It is an output signal waveform diagram, and (d) an output signal waveform diagram of the selection unit. FIGS. 5A to 5C are equivalent to FIGS. 4A to 4C with sampling points added. Further, in FIG. 5D, even when a normal audio signal can be output at timing T4, the audio signal newly demodulated from the audio signal interpolated into an abnormal interval as shown in FIG. Instead of switching, the audio signal gradually interpolated over the period T4 to T5 is switched to the audio signal newly demodulated by the demodulator and output. Specifically, the interpolated audio signal and the newly demodulated demodulated audio signal are respectively weighted, and a new time is added from the audio signal interpolated from the timing T4 to the timing T5 and the weighting specific gravity is interpolated from the timing T4. The audio signal demodulated after T4 is transferred, and the audio signal obtained by taking the specific gravity average of both is output in the section from timing T4 to timing T5.

  FIG. 6 is a diagram for explaining an image of specific gravity average processing according to an embodiment of the present invention in which the timing T4 to the timing T5 are further expanded. In FIG. 6, reference numeral 601 denotes the level of the interpolated voice signal that is output during a period in which the voice signal is abnormal, 603 denotes the level of the voice signal demodulated after the voice signal is restored from the abnormal state, and 602 denotes 601. 603 is the audio signal level obtained by taking the specific gravity average of both. If the level difference between the level of the specific gravity average signal 602 and the level of the demodulated signal 603 is X, and the level difference between the level of the interpolation signal 601 and the level of the specific gravity average signal 602 is Y, the interpolation in the specific gravity average signal 602 is performed at timing T4. The specific gravity of the signal 601 and the demodulated signal 603 is “1” vs. “0”. Therefore, the specific gravity average signal 602 is equal to the level of the interpolation signal 601, and when the level difference X = 1 between the demodulated signal 603 and the specific gravity average signal 602, the level difference Y = 0 between the interpolation signal 601 and the specific gravity average signal 602. is there.

  Thereafter, the specific gravity of the interpolation signal 601 is decreased from T4 to T5, and the specific gravity of the demodulated signal 603 is increased. Then, the specific gravity average signal 602 of both approaches the demodulated signal 603 gradually from the interpolation signal 601.

  At timing T5, the specific gravity of “interpolation signal 601” vs. “demodulation signal 603” in the specific gravity average signal 602 is “0” vs. “1”. Accordingly, the level of the specific gravity average signal 602 is equal to the level of the demodulated signal 603, the level difference X = 0 between the demodulated signal 603 and the specific gravity average signal 602, and the level difference Y = 1 between the interpolation signal 601 and the specific gravity average signal 602. It becomes. By the above processing, since the interpolation signal 601 is gradually shifted from the demodulated signal 603, it is possible to prevent the generation of a harsh sound (noise) as shown in FIG. 4D.

  Next, an example of a specific configuration of the FM receiver that realizes the specific gravity average process will be described. FIG. 1 is a block diagram of an entire FM receiver according to Embodiment 1 of the present invention. FIG. 1 shows an FM receiver for receiving an audio signal of TV broadcasting. In TV broadcasting, a video signal and an audio signal are mixed in a predetermined frequency band (channel), placed on a carrier wave, and transmitted as a broadcast signal. Broadcast signal 131 is received by antenna 111 and input to TV tuner 112. The TV tuner 112 extracts a video signal and an audio signal from a desired frequency band (channel). Since the audio signal has a frequency band between the own channel and the next channel, the audio signal is extracted by a band pass filter BPF included in the tuner 112. The extracted audio intermediate frequency signal (SIF) 132 is output from the TV tuner 1112 and input to the analog / digital converter (A / D converter) 113.

  The A / D converted digital audio intermediate frequency signal (SIF) 133 is input to a demodulator (FM detector) 101 and an anomaly detector (SIF anomaly detection circuit) 102. The demodulator 101 performs FM detection and demodulation on the audio signal 134 from the audio intermediate frequency signal 133. The abnormality detection unit 102 detects an abnormality in the audio intermediate frequency signal 133 and controls the interpolation process when an abnormality is detected. When the audio intermediate frequency signal 133 is abnormal, the holding unit 103, the specific gravity average processing unit 107, and the selection unit 106 perform the interpolation process and the recovery process from the interpolation process without outputting the audio signal demodulated by the demodulation unit 101 as it is. Do. The holding unit 103 holds the audio signal demodulated by the demodulation unit 101 or the audio signal output by the previous interpolation process. When the audio intermediate frequency signal 133 recovers from an abnormal state to a normal state, the specific gravity average processing unit 107 performs specific gravity average processing that gradually switches from the interpolated signal to a newly demodulated signal after recovery by the demodulation unit. The selection unit 106 includes three audio signals: an audio signal 134 demodulated by the demodulation unit 101, an audio signal 137 held by the holding unit 103, and an audio signal 138 obtained by taking the specific gravity average of the audio signals 134 and 137 by the specific gravity average processing unit 107. One audio signal 135 is selected from 134, 137, and 138 and output.

  The D / A converter 114 converts the digital audio signal 135 into an analog audio signal 136. The speaker 115 converts an analog audio signal 136 that is an electrical signal into audio. The holding unit 103 includes a pre-selection unit 104 that is a selector and a flip-flop circuit 105 that holds data. The pre-selection unit (selector) 104 is output from the audio signal 134 output from the demodulation unit 101 and the selection unit 106. Any audio signal 135 to be selected is selected and sent to the flip-flop circuit 105. The flip-flop circuit 105 temporarily holds data output from the preselection unit 104.

  Of the components of the FM signal receiving apparatus 100 shown in FIG. 1, the configuration from the A / D converter 113 to the D / A converter 114 excluding the antenna 111, the TV tuner 112, and the speaker 115 is one. It can be easily configured as a one-chip semiconductor integrated circuit formed on a semiconductor substrate. By using a single chip, it is possible to perform faster data processing with lower power consumption.

  Next, the operation of the FM signal receiving apparatus 100 in FIG. 1 will be described with reference to the flowchart for explaining the audio data processing method in FIG. It is assumed that there is no abnormality in the amplitude of the intermediate frequency signal 133 in the initial state. At this time, in FIG. 1, the preselection unit 104 and the selection unit 106 select the audio signal 134 output from the demodulation unit 101. In step S <b> 1 of FIG. 8, the A / D converter 113 receives the analog audio intermediate frequency signal 132 and converts it into a digital audio intermediate frequency signal 133. In step S2, the abnormality detection unit 102 measures the amplitude of the digital audio intermediate frequency signal 133. Since there is no abnormality in the waveform of the intermediate frequency signal 133, the abnormality detection unit 102 determines in step S3 that there is no abnormality in the amplitude of the intermediate frequency signal 133 (determined No). Also, the abnormality detection unit 102 is set so that both the preselection unit 104 and the selection unit 106 select the audio signal 134 output from the demodulation unit by the selection unit control signal 139 by the initial setting. In step S4, the demodulator 101 performs FM demodulation and outputs an audio signal 134. In step S5, the holding unit 103 takes in the audio signal 134 and updates the data held in the flip-flop circuit (F / F) 105. The digital audio signal 134 demodulated by the demodulator 101 is converted into an analog audio signal 136 by the D / A converter 114 via the selector 106 and output as audio from the speaker 115 (step S6). The processing from step S1 to step S6 is repeated until the amplitude of the intermediate frequency signal 133 becomes abnormal at timing T1 in the waveform diagram of FIG.

  When the timing T1 in FIG. 5A is reached and the amplitude of the intermediate frequency signal 133 becomes abnormal, the abnormality detection unit 102 detects an abnormality in step S3 in FIG. 8 (determined as Yes). If it is determined as Yes in step S3, the abnormality detection unit 102 outputs the selection unit control signal 139 at the timing T3 when the demodulation unit 101 starts outputting an abnormal audio signal (step S7). In response to the selection unit control signal 139, the selection unit (selector) 106 switches the input data from the digital audio signal 134 demodulated by the demodulation unit 101 to the digital audio signal held by the flip-flop circuit 105, and the pre-selection unit The (selector) 104 switches the input data from the digital audio signal 134 demodulated by the demodulator 101 to the digital audio signal 135 selected by the selector 106 (step S8). The timing at which the preselection unit 104 and the selection unit 106 switch in response to the selection unit control control signal is timing T3.

  When the selection unit 106 switches the input data from the audio signal 134 demodulated by the demodulation unit 101 to the audio signal 137 output from the flip-flop circuit 105, the audio signal 137 held by the flip-flop circuit 105 is used instead of the audio signal 134. (Step S9). The audio signal 137 is further converted into an analog audio signal 136 by the D / A converter 114 and output as audio from the speaker 115 (step S10). Here, the output of the interpolated audio signal stored in the flip-flop circuit 105 is repeated until the amplitude abnormality is recovered (determined No in step S11).

  In FIG. 5A, when the timing T2 is reached and recovery from the abnormal amplitude is made, the demodulator 101 determines the timing T4 at which the output of the normal audio signal 134 starts and determines Yes in step S11, and then step S12. Proceed to

  In step S12, the abnormality detection unit 102 outputs the selection unit control signal 139. The selection unit 106 receives the selection unit control signal 139 and switches the input signal to the digital audio signal 138 output from the specific gravity average processing unit 107 (step S13). On the other hand, the A / D converter 113 converts the analog audio intermediate frequency signal 132 after recovery from the abnormality into a digital audio intermediate frequency signal 133 (step S14). In response to this, the demodulator 101 performs FM demodulation and outputs a demodulated digital audio signal 134 (step S15). The specific gravity average processing unit 107 receives the demodulated digital audio signal 134 output from the demodulation unit 101 and the digital audio signal 137 output from the holding unit 103, and obtains the specific gravity average of both by calculation (step S16). The digital audio signal 138 output from the specific gravity average processing unit 107 is taken into the flip-flop circuit 105 of the holding unit 103 via the selection unit 106 and the pre-selection unit 104, and the data held by the flip-flop circuit 105 is updated ( Step S17). Further, the digital audio signal 138 output from the specific gravity average processing unit 107 is selected by the selection unit 106 and input to the D / A conversion unit 114, further converted into an analog audio signal 136 and output from the speaker 115 as audio (step). S18).

  The processing from step S14 to step S18 is repeated until the averaging processing is completed at timing T5 in the waveform diagram of FIG. 5 (in the case of No in step S19). In the averaging process, the specific gravity average processing unit 107 shifts the specific gravity to be averaged from the audio signal 137 held by the holding unit 103 (flip-flop circuit 105) to the audio signal newly demodulated by the demodulation unit 101. When the averaging process of the specific gravity average processing unit 107 is completed (Yes in step S19), the selection unit (selector) 106 and the pre-selection unit (selector) 104 are converted into the demodulated audio signal 134 of the demodulator 101. Switch to the initial state (step S20). The above process is repeated to perform audio playback processing.

  Next, the abnormality detection operation of the abnormality detection unit 102 shown in FIG. 1 will be described in more detail. The abnormality detection unit 102 investigates the peak-to-peak amplitude of the digital audio intermediate frequency signal 133, and determines that it is abnormal when the value falls below a certain threshold value several times. In FM modulation, the amplitude of the intermediate frequency signal does not occur depending on the volume, so that the amplitude is always constant. From this, it is considered that a normal intermediate frequency signal is inputted if the amplitude shows a substantially constant value for each cycle. FIG. 3A shows a normal FM-modulated audio intermediate frequency signal SIF having a constant amplitude, and FIG. 3B shows an audio intermediate frequency signal SIF at the time of abnormality in which the amplitude is suddenly interrupted.

  In the waveform of FIG. 3B, the portion 301 indicates a sufficient amplitude and exceeds the threshold 303, so that the abnormality detection unit (SIF abnormality detection circuit) 102 determines that it is normal. However, at the portion 302 where the amplitude is abnormally small, the amplitude of the audio intermediate frequency signal SIF is interrupted and is smaller than the threshold 303. Therefore, for example, when the amplitudes below points A and B and the threshold value 303 in FIG. In addition, when the abnormality detection unit 102 detects an amplitude abnormality, the number of detections and the level of the threshold 303 can be arbitrarily set as necessary.

  Next, the specific gravity average process performed by the specific gravity average processing unit 107 will be described in more detail. The specific gravity average processing unit 107 calculates a specific gravity average of the normal audio sampling data 134 demodulated by FM and the data 137 stored in the flip-flop circuit 105. The calculation method of specific gravity average is as follows (Formula 1).

  D = (Xa + Yb) / R, X + Y = R (Formula 1)

  Here, D is output data, X and Y (positive numbers) are ratios, a is data stored in the flip-flop circuit, b is FM demodulated sampling data, and R is bit width. Here, the bit width R = 16.

  An example of performing the specific gravity average processing according to the above (Formula 1) is shown in Table 1 below and FIG. In Table 1, a, b, X, and Y are numerical values to be assigned to (Equation 1), and the calculation result D of (Equation 1) is shown as an output. In the data plotted in FIG. 7, “demodulation output” is the value of b, and “specific gravity average output” is the value of the calculation result D. In FIG. 7, it is assumed that the time value on the X axis is equal to the Y value.

  At the start of the specific gravity averaging process, a value of 10 is stored in the flip-flop circuit 105, and normal sampling data immediately after switching from normal to normal is assumed to be 4. Since a is data stored in the flip-flop circuit 105, when it is in an abnormal state, the value 10 immediately before becoming abnormal is maintained and 10 is always output. Since b is demodulated data, assuming that it is output with a curve as shown in “Demodulated output” in FIG. 7, the output is 4, 3, 2,... Is done. Immediately after the selection unit 106 switches to the output data of the specific gravity average processing unit 107, a = 10, b = 4, and the ratio of X and Y is calculated as X: Y = 16: 0. Since the ratio on the b side is 0, the value on the a side becomes the output D as it is, and D = 10. The output is stored in the flip-flop circuit 105. At the next sampling, a = 10, b = 3, and the ratio is X: Y = 15: 1. Since the weight is also given to the b side this time, the output D becomes D = 9.5625 by the calculation of (Equation 1). The current output D is stored in the flip-flop circuit 105, that is, 9.5625 is stored. Next, a = 9.5625 and sampling data b = 2 stored in the flip-flop circuit 105 are calculated. According to (Equation 1), the output D becomes D = 8.617188. When these processes are repeated and averaged, a waveform like “specific gravity average output” in FIG. 7 is output.

  It can be seen that this waveform is output while approaching the waveform of "FM demodulated sampling data" (normal audio data) with a smooth change. By including such a process, it is possible to perform an interpolation process without a sudden change in the sound level, so that it is not necessary to output an audible sound (noise). When the processing from X: Y = 16: 0 to 0:16 is finished, the specific gravity average processing is finished.

  In FIG. 6, the level of the data 601 to be held does not change during the specific gravity average process. However, in the circuit of FIG. 1, the data held in the holding unit 103 is updated by performing the specific gravity average process. Therefore, the result of taking the specific gravity average shown in FIG. 7 is slightly different from FIG. However, in both cases, there is no change in that the specific gravity average processing is performed to gradually and smoothly shift from the data interpolated at the time of abnormality to the data demodulated after recovery. In the circuit of FIG. 1, if data is taken into the flip-flop circuit 105 only when the abnormality detection unit 102 detects that the timing becomes a new abnormality, interpolation as shown in FIG. 6 is performed. You can also.

  Further, in the above embodiment, the specific gravity average processing unit 107 has the function of the selection unit 106, the selection unit 106 is omitted, and the audio signal 134 demodulated by the demodulation unit 101 from the specific gravity average processing unit 107 and the holding unit 103. Either the audio signal 137 held by the audio signal or the audio signal obtained by taking the specific gravity average of both may be output.

  The holding unit holds the audio digital signal as a waveform approximated by, for example, a Fourier series, and the specific gravity average unit calculates the specific gravity average of the waveform of the audio signal demodulated by the demodulation unit and the waveform held by the holding unit, It is also possible to output as a signal.

  Although the embodiments have been described above, the present invention is not limited only to the configurations of the above embodiments, and of course includes various modifications and corrections that can be made by those skilled in the art within the scope of the present invention. It is.

  The present invention is particularly effective for demodulation when an audio signal is overmodulated in reception of a TV broadcast, but is not limited thereto. The present invention is not limited to FM monaural broadcasting, and can also be applied to FM stereo broadcasting and FM dual broadcasting. This is generally effective for reproducing an audio signal that is excessively FM modulated. Furthermore, the present invention is not limited to FM modulation, and can be used when demodulating an audio signal and interpolating and reproducing the audio signal as comfortably as possible when the audio signal becomes abnormal.

100: FM signal receiver 101: Demodulator (FM detector)
102: Abnormality detection unit 103: Holding unit 104: Preselection unit (selector)
105: Flip-flop circuit (F / F)
106: Selection unit (selector)
107: Specific gravity average processing unit 111: Antenna 112: TV tuner 113: A / D converter 114: D / A converter 115: Speaker 120: Semiconductor integrated circuit 131: Broadcast signal (FM signal) received by the antenna
132: Analog voice intermediate frequency signal 133: Digital voice intermediate frequency signal 134: Digital voice signal demodulated by demodulator 135: Digital voice signal selected by selector 136: Analog voice signal 137: Digital voice signal held by holder 138 : Digital audio signal with specific gravity average taken by specific gravity average processing unit 139: Selection unit control signal 201, 203: Video signal 202, 204: Audio signal 251: Frequency band FM-modulated beyond bandpass filter BPF band 301: Normal intermediate frequency signal amplitude (peak-to-peak)
302: Abnormal intermediate frequency signal amplitude (peak-to-peak)
303: Determination level (threshold value) of intermediate frequency signal
601: Signal level demodulated by demodulator immediately before detecting abnormality (signal level held by holding unit)
602: Output signal level of specific gravity average part 603: Signal level demodulated by demodulator immediately after recovery from abnormality T0: Reception start timing T1: Timing at which intermediate frequency signal becomes abnormal from normal T2: Intermediate frequency signal from abnormal to normal Return timing T3: Timing at which the audio signal demodulated by the demodulation unit becomes normal to abnormal T4: Timing at which the audio signal demodulated by the demodulation unit returns from normal to normal T5: Timing at which the specific gravity average processing unit completes the specific gravity average processing

Claims (16)

A demodulator that demodulates the audio signal;
An abnormality detection unit for detecting that the audio signal becomes abnormal;
Input a voice signal demodulated by the demodulator, and a holding unit that holds a voice signal before detecting an abnormality at least during a period in which the abnormality detector detects an abnormality,
An audio signal newly demodulated by the demodulator and an audio signal held by the holding unit are input, and after recovering from the abnormality, the audio signal demodulated by the demodulator from the audio signal held by the holding unit Specific gravity average processing section that gradually switches to
An audio signal processing device comprising: The demodulator detects and demodulates the audio signal from the FM modulated audio intermediate frequency signal;
The audio signal processing apparatus according to claim 1, wherein the abnormality detection unit detects that the audio signal becomes abnormal by inputting the audio intermediate frequency signal.   The processing time required for detecting that the audio signal becomes abnormal after the abnormality detection unit inputs the audio intermediate frequency signal is shorter than the processing time required for the demodulation unit to demodulate the audio signal from the audio intermediate frequency signal. 3. The audio signal according to claim 2, wherein the holding unit holds an audio signal immediately before the demodulation unit starts outputting an abnormal audio signal after the abnormality detecting unit detects the abnormality. Processing equipment.   The specific gravity average processing unit weights the audio signal held by the holding unit and the audio signal demodulated by the demodulation unit, and the demodulating unit calculates the weighted specific gravity from the audio signal held by the holding unit. 4. The audio signal processing apparatus according to claim 1, wherein the audio signal is gradually shifted to the audio signal to be demodulated and averaged, and the averaged audio signal is output.   A selection unit that selects and outputs one of three audio signals: an audio signal newly demodulated by the demodulation unit, an audio signal held by the holding unit, and an audio signal output by the specific gravity average processing unit The audio signal processing apparatus according to claim 1, further comprising: The selection unit includes:
When the abnormality detection unit has not detected an abnormality, the demodulation unit newly selects and outputs the audio signal to be demodulated,
While the abnormality detection unit detects an abnormality, the audio signal held by the holding unit is selected and output,
6. The audio signal processing apparatus according to claim 5, wherein after the abnormality detection unit detects recovery from the abnormality, the audio signal output by the specific gravity average processing unit is selected and output for a certain period. The holding part is
When the abnormality detection unit has not detected an abnormality, the demodulating unit updates the data held by the audio signal newly demodulated,
When the specific gravity average processing unit performs a process of gradually switching from the audio signal held by the holding unit to the audio signal demodulated by the demodulation unit and outputting the audio signal, the audio signal output by the specific gravity processing average processing unit The audio signal processing apparatus according to claim 1, wherein the data held by the update is updated. The holding unit includes a preselection unit that selects an audio signal output from the demodulation unit and an audio signal output from the selection unit, and a flip-flop in which data is updated by the audio signal selected by the preselection unit With circuit,
The preselection unit selects an audio signal output from the demodulation unit when the abnormality detection unit does not detect abnormality, and when the abnormality detection unit detects abnormality and the specific gravity average process 7. The audio signal processing according to claim 5, wherein the audio signal output from the selection unit is selected when the unit is gradually switching from the audio signal of the holding unit to the audio signal of the demodulation unit. apparatus. The demodulator detects and demodulates the audio signal from the FM modulated audio intermediate frequency signal;
The audio signal according to any one of claims 1 to 8, wherein the abnormality detection unit receives the audio intermediate frequency signal and detects an abnormality when the amplitude of the audio intermediate frequency signal is abnormally small. Processing equipment.   10. The audio signal processing apparatus according to claim 9, wherein the abnormality detection unit detects an abnormality when the amplitude of the audio intermediate frequency signal is continuously lower than a predetermined threshold value a predetermined number of times. .   11. An audio signal processing device according to claim 1, wherein the audio signal processing device is integrated and formed on a single semiconductor substrate. A tuner that receives an FM signal and outputs an intermediate frequency signal;
An AD converter for converting the intermediate frequency signal into a digital intermediate frequency signal;
An FM detector for detecting a digital audio signal from the digital intermediate frequency signal;
An intermediate frequency abnormality detection unit for detecting an abnormality of the digital intermediate frequency signal;
While the intermediate frequency abnormality detection unit is detecting an abnormality, a holding unit that holds the digital audio signal before detection;
After recovering from the abnormality, a specific gravity average processing unit that gradually switches and outputs a digital audio signal held by the holding unit to a digital audio signal newly detected by the FM detector;
A DA converter for converting the digital audio signal into an analog audio signal;
FM signal receiving apparatus.   A selection unit that selects one of the digital audio signal held by the holding unit, the digital audio signal processed by the specific gravity average processing unit, and the digital audio signal output by the FM detection unit, and outputs the selected signal to the DA converter; 13. The FM signal receiver according to claim 12, further comprising:   The FM signal receiver according to claim 12 or 13, wherein the tuner is a TV tuner.   The AD converter, the FM detector, the intermediate frequency abnormality detection unit, the holding unit, the specific gravity average processing unit, and the DA converter are integrated on a single semiconductor substrate. The FM signal receiving apparatus according to claim 12, wherein the FM signal receiving apparatus is provided. When there is no abnormality in the audio data signal, the audio data signal is demodulated and output,
When there is an abnormality in the audio data signal, output the demodulated signal before becoming abnormal,
When the abnormality of the audio data signal is recovered, the signal demodulated before the abnormality is recovered and the demodulated signal after the abnormality is recovered are respectively added by weighting, and the weight ratio is set before the abnormality is recovered. By gradually shifting to the demodulated signal after the abnormality is recovered from the demodulated signal, the demodulated signal is smoothly shifted to the demodulated signal after the abnormality is recovered before becoming abnormal. A method of processing audio data in an audio signal processing apparatus.

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